FR2571051A1 - PROCESS FOR SYNTHESIZING THIOGLYCOLIC ACID - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR SYNTHESIS OF THIOGLYCOLIC ACID. ACCORDING TO THE INVENTION, CONTACT IS IN A REACTION ZONE UNDER A HIGH PRESSURE OF AT LEAST 17 BARS FORMED BY HYDROGEN SULFIDE GAS, A MIXTURE OF MONOCHLOROACETIC ACID AND DICHLOROACETIC ACID OR THEIR METAL SALTS ALKALINS HAVE A WEIGHT RATIO OF 99: 1 TO 75:25 WITH A HYDROSULFIDE OF AN ALKALINE OR ALKALINO-EARTH METAL SO THAT THE MOLAR RATIO OF METAL HYDROSULFIDE TO MONOCHLOROACETIC ACID IN THE FORM OF FREE ACID IS D 'AT LEAST 2.1 AND WITH DICHLOROACETIC ACID OR AT LEAST 3.1; THE LIQUIDS PRODUCED ARE SEPARATED AND THE THIOGLYCOLIC ACID IS RECOVERED. THE INVENTION APPLIES IN PARTICULAR TO THE PRODUCTION OF WAVING PREPARATIONS FOR THE HAIR, OF COSMETIC DEPILATORIES AND FOR TRADE AGENTS USED TO REMOVE THE HAIR FROM STAINS AND THE LIKE.

Description

The present invention is directed to a process for forming acid

thioglycolic to high

  yields by reaction of mixtures of monochloro-

  acetic acid and dichloroacetic acid with a hydrosulfide of an alkali metal under the conditions described below. Thioglycolic acid is a very desired product having various commercial applications. It forms the active ingredient of most hair ripple preparations. It is also used extensively in cosmetic depilatories and in commercial agents used to remove hair from bodies and the like. Various other commercial uses are made of thioglycolic acid in addition to those described above. The large and varied demands for thioglycolic acid strongly require the formation of this material by the most effective method.

efficient and the most economical.

  Thioglycolic acid is currently prepared commercially by reaction of monochloroacetic acid

  pure with sodium hydrosulfide in an aqueous medium.

  After acidification, the thioglycolic acid is extracted from the reaction mixture with a suitable organic solvent and is purified by distillation. This process first

  was described by Carius in Ann. 124, 43 (1862) and later

  perfected by Klason and Carlson in Ber. 39

  732-738 (1906). These latter authors have taught that

  The process was best carried out using a sodium hydrosulfide liquor of not more than 15% by weight and a solution of weak monochloroacetic acid containing

  the acid at not more than 20% by weight.

  Other methods have been suggested. These include a two-step synthesis of initially reacting the monochloroacetic acid with sodium thiosulfate followed by hydrolysis of the resulting Bunte salt (see US Patent Nos. 2,594,030; 2,413,361 and British Patent 624,568). Another proposed synthesis (German Patent No. 180,875) comprises reacting the monochloroacetic acid with an alkali polysulfide and then reducing the dithiodiglycolic acid formed by means of zinc and a mineral acid. US Patent 3,860,641 discloses a method of. formation of thioglycolic acid by heating an alkaline hydrosulfide

with a xanthogenic acid.

  Recent patents directed to changes in

  Klonson and Carison's process for forming thioglycolic acid include US Pat. Nos. 3,927,085 and 4,082,790. US Pat. No. 3,927,085 discloses a modification which requires the presence of aqueous hydroxide of sodium hydroxide or ammonium hydroxide. sulphide partial pressure

  of hydrogen and monochloroacetic acid or monochloro-

pure propionic at 4-12 mole%.

  US Pat. No. 4,082,790 teaches that mono-, di- or trimercaptans of formula R (SH) a can be formed by reaction of mono-, di- or trichloride or bromide, R (X) a with H 2 S and ammonia or an amine in aqueous systems to give the corresponding mercaptan R (SH) a. R can represent an aliphatic carboxylic acid and a represents a number

integer from 1 to 3.

  The most commonly used method is

  described by Klason and Carlson. The starting carboxylic acid is pure monochloroacetic acid either under the

  form of the free acid or its salt of an alkali metal.

  The acid feed must be free of polyhaloacids to prevent the formation of the corresponding polythiols

  as suggested in US Patent 4,082,790.

  Since chloroacetic acid normally forms as a mixture of mono- and dihaloacids, the currently known technique requires the separation and purification of monochloroacetic acid prior to use in order to obtain high yields of the monochloroacetic acid.

desired product.

  It would be highly desirable to have a desired thioglycolic acid forming process using a combination of mono- and polychloroacetic acids as a food reagent. Such a process would provide a more efficient and economical mode of

desired product.

  The present invention is directed to a process for forming thioglycolic acid in high yields by reacting, in an aqueous medium and at an elevated pressure of at least 17 bar, a mixture of mono- and dichloroacetic acids with carbon dioxide. sodium hydrosulfide under the conditions described below. The present process provides a means for obtaining very high yields of the desired product while using a

  mixture of substituted acetic acids into chloride.

  This process eliminates the previously required purification of monochloroacetic acid for use as a feed in the commercial formation of

thioglycolic acid.

  Halogenated organic acid as feedstock

  used in the present process is a mixture

  of monochloroacetic acid and dichloroacetic acid.

  The weight ratio of mono- to di-

  Substituted in the feedstock can range from about 99: 1 to 75:25, preferably from about 98: 2 to 95: 5. The inclusion of dichloroacetic acid as a part of the feed burden has been unexpectedly shown in the present conditions not to be harmful but, on the contrary, to assist production.

  thioglycolic acid at high yields.

  The feedstock of mixed organic acids can be introduced into the reaction zone, as described below, in an aqueous medium. The concentration of the mixed organic acid filler can be any concentration that produces a homogeneous liquid phase under the reaction conditions. The feedstock of organic acids can be from about 35% by weight, preferably from about 20 to 35% by weight based on the introduced aqueous liquid system.

in the reaction zone.

  The feedstock of mixed organic acids can be introduced as free acids. The free acid is the preferred feedstock although the acids may be partially or completely in the form of their alkali metal salt, such as sodium, upon introduction into the reaction zone. The reactive hydrosulfide of an alkali metal or alkaline earth metal can easily be formed in known ways. It is preferable to use sodium hydrosulfide although other alkali metal hydrosulfides, such as potassium hydrosulfide or

  alkaline earth metal hydrosulphides such as hydro-

  Calcium sulphide may be used. The hydrosulfide of an alkali or alkaline earth metal must be at water-soluble concentrations of 7 to about 40% by weight and preferably 25 to 35% by weight in the water.

  aqueous system in the reaction zone.

  The aqueous feeds of (1) the mixed chloroacetic acids and (2) the hydrosulfide of a metal must be introduced into the reaction zone so that there is a molar excess of

  the hydrosulfide of a metal with mono- and dichloro-

  mixed acetics. The molar ratio of a metal hydrosulfide to monochloroacetic acid (as free acid) in the feed load shall be at least 2.1 or, when supplied in the form of a salt,

  must be at least 1.1. The molar ratio of hydro-

  sulphide from a metal to dichloroacetic acid (in the form of free acid) in the feed load must be at least 3.1 and if supplied in the form of salt, must be at least 2.1. Higher gear can be used. The preferred molar ratio of a metal hydrosulfide to monochloroacetic acid is from 2.1 to about 3 and dichloroacetic is from about 3.1 to about 4. Still higher ratios

can be used.

  The reaction is carried out at a pressure of at least 17 bar and pressures of 17 to 34 bar have been found to produce the best yields it is critical that the reaction be carried out at the described high pressures of hydrogen sulfide to force the process to proceed. produce the desired product at high yields. The pressure can be obtained by the autogenous pressure of the reagents or with the addition of sulphide

  additional hydrogen gas.

  In contrast to the criticality of the high pressure conditions, it has been observed that when the present reagents are used, the reaction can be carried out at low temperatures. The reaction may be carried out at temperatures from room temperature to about 150 ° C and preferably from room temperature to 100 ° C and more preferably from room temperature to 60 ° C. The ability to perform the process at low temperatures another beneficial aspect of the invention to unexpectedly produce a

economically efficient process.

  The time during which the reagents are contained in the reaction zone can be easily determined by those skilled in the art in order to optimize the yield. Normally, the time will vary depending on the size and configuration of the reactor and whether the process is performed batchwise or continuously. Normally, residence times of at least about 20 minutes give good yields with times greater than about 40 minutes showing

  substantially no further increases in

  ments. Larger or smaller times may be appropriate under various conditions of the reaction zone. The reaction zone may be any reactor capable of causing contact among the reactants in a batch or continuous process. For example, a conventional tubular reactor or its equivalent can be used to carry out the reaction in a continuous manner while a reaction vessel under pressure

  can be used for a batch operation.

  Feed streams (one containing a mixture of organic acids and one containing an alkali metal hydrosulfide) can be mixed before entering the reaction zone. The mixture can be accomplished

  by various conventional means for a liquid mixture

  liquid like vortex mixers or static mixers with coils made of stainless steel cloth or the like. The mixed feeds are introduced into a reaction zone. When the process is carried out on a continuous basis, a high pressure metering pump or the like can be used to introduce the feed fluids into the reaction zone at a rate such that the reactants are maintained in the reaction zone for a period of time. sufficient residence to allow the reactants to form the produced thioglycolic acid in high yields. The reaction zone must be maintained at a pressure of at least 17 bar (preferably 17 to 34 bar) and may be at temperatures between room temperature and about 150 C (preferably room temperature to 100 C and better) temperature

  ambient at 80 C) as described above.

  The liquid material is removed from the reaction zone. For example in a continuous process, the removal can be carried out by expanding the liquid through a back pressure regulator or the like at atmospheric pressure. The exhaust gases that are produced in the reactor (mainly H25) are then removed and normally pass through

caustic purifiers.

  The aqueous liquid removed from the reaction zone contains thioglycolic acid as the main reaction product (yield normally greater than 90%) and may also contain minor amounts of thioglycolic acid as a by-product. The liquid removed from the reaction zone can be treated with an inorganic mineral acid such as sulfuric acid to convert the alkali metal salts of organic acids to free acid. It has also been unexpectedly found that the major by-product thiodiglycolic acid, could

  removed, recycled and introduced into the reaction zone

  as part of the feedstock.

  When recycling thiodiglycolic acid

  produced under the conditions of the process of the present invention, total yields of the desired product of about 95-100% o are obtained. The training hypothesis

  thioglycolic acid from thio-

  diglycolic acid is the following (this theory is in no way considered to limit the present invention but

  simply as a suggested mode) by the disproportionate

  Thiodiglycolic acid according to the following reaction: NaOOCCH2SCH2COONa + H2S 2 HSCH2COONa The following examples are for illustrative purposes only and should not be used in any way.

  case limit the attached claims. All parties

  and percentages are by weight unless it is

otherwise indicated.

EXPERIENCE

  The process was accomplished in a continuous manner using a tubular reactor. It consisted of a tubular reactor 5.18 meters long, 3.17 mm internal diameter and 6.35 mm outer diameter wound in a spiral so as to fit in an oil bath at high temperature. The temperature of the bath, T2 and that of the product, T1 were very precisely monitored by two thermocouples and controlled by an automatic temperature controller. The pressure of the system

  the reactor was controlled by a counter-pres-

  at a range of 0-34 bar and was precisely monitored by two manometers, at a range of 0-41 bar,

  placed at the inlet and outlet of the tubular reactor.

  The alkali metal hydrosulfide (in the form of NaSH) and the mono and dichloroacetic acids mixed as feedstocks were fed to the tubular reactor from tanks by means of separate two-piston high pressure metering pumps having flow of 0.12 m / min to 3.6 mQ / min per head. The feeds were initially mixed using a two-tube mixer. The NaSH stream was introduced through the insertion charge tube with

  the organic acid stream from the outside.

  The two streams were then passed through a static mixer having coils of a gauze

  of stainless steel to obtain a wider mixture.

  The liquid phase product of the reactor was expanded by a back pressure regulator at atmospheric pressure. It was then acidified with 75% sulfuric acid before being collected in a receptor.

  stainless steel. The exhaust gases were then passed

  through two caustic cleaning solutions in series to remove hydrogen sulphide. Samples of the liquid product were analyzed by a standard technique for thioglycolic acid (TGA),

  thiodiglycolic acid (TDGA) and dithiodic acid

  glycolic acid (DTDGA) using high pressure liquid chromatography. Thioglycolic acid can be

  recovered by extraction using methylisobutyl-

ketone with then distillation.

  Using the device described above, a series of tests were conducted using a commercial mixture of monochloroacetic acid (MCA) and acid.

  dichloroacetic acid (DCA) at a molar ratio of 97: 3.

  Each reaction was carried out at a pressure of 28 bar (inlet and outlet pressure) and a residence time of 40 minutes. The temperature of the tests changed between C and 80 C by monitoring the reaction and exit temperature. The results of the tests are given in

Table I below.

TABLE I

  MCA Temperature Test DCA NaSH TGA TDGA DTDGA C Concentration% Molar Yield

1 25 3.0 0.09 6.6 91.4 4.5 -

2 50 3.0 0.09 6.6 87.3 6.3 -

3 80 3.0 0.09 6.6 90.3 8.6 -

EXAMPLE II

  A series of tests were conducted in the same manner as described in Example I above except that the temperature was maintained at 25 ° C. while the pressure was varied in the reaction zone at each test. The results given in Table II below show that the present process should be carried out at a high pressure of at least about 17 bar (mainly due to H 2 S) to produce the desired thioglycolic acid at high yields. Reactions at lower pressures (even at much longer reaction times)

  do not produce the desired high yields.

Table II

  Test Temperature Pressure Time of Performance C bars residence TGA% O (mn)

4 25 0 70 57

25 10 70 88

6 25 17 40 92

7 25 28 40 95

EXAMPLE III

  A series of tests is carried out in the same manner as described in Example I above with the exception that the glycolic acid thioether (TDGA) is recovered as a distillation residue, after distillation and recovery of thioglycolic acid. The recovered thioether is reintroduced into the reaction zone as part of the mixed organic acid feed stream. The total yield resulting from the thioglycolic acid produced is

increased by about 3.5 to 5%.

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Claims (11)

R E V E N D I C A T I 0 NS   1. A process for the synthesis of thioglycolic acid, characterized in that it consists in bringing into contact, in a reaction zone, with a high pressure of at least 17 bar formed by hydrogen sulphide gas, a   mixture of monochloroacetic acid and dichloroacetic acid   acetic acid or their alkali metal salts in a weight ratio of 99: 1 to 75:25 with a hydrosulfide of an alkali or alkaline earth metal so that the ratio   molar of said metal hydrosulfide to monochloro   acetic acid in the form of free acid of at least 2.1 and dichloroacetic acid of at least 3.1; separating the liquids produced and recovering the thioglycolic acid. 2. A process according to claim 1, characterized in that the pressure in the reaction zone is between 17 and 34 bars.   3. Process according to claim 1, characterized in that the temperature of the reaction zone is   between room temperature and about 150 C.   4. Process according to claim 2, characterized in that the temperature in the reaction zone is   between room temperature and about 100 C.   5. A process according to claim 1, characterized in that the ratio of the hydrosulfide of a metal to the combined mixture of mono- and dichloroacetic acids is   from 2.1 to about 3 with respect to monochloro   acetic component and from 3.1 to about 4 for acid dichloroacetic component.   6. A process according to claim 1, characterized in that the ratio of hydrosulfide to mono- and dichloroacetic acid combined in the form of acidic salt is from 1.1 to about 1.9 and in that said hydrosulfide is introduced into the reaction zone in form sodium hydrosulfide. -271051   7. Process according to any one of   1, 2 or 6, characterized in that the   molar ratio of monochloroacetic acid to acid   dichloroacetic acid is from 99: 1 to 75:25.   8. Process according to any one of   1, 2 or 6, characterized in that the   molar ratio of monochloroacetic acid to acid   dichloroacetic acid is from 98: 2 to 95: 5.   9. A process according to claim 1, characterized   in that it also includes separation and recuperation   the thiodiglycolic acid of the liquids produced in the reaction zone and the reintroduction of at least a portion of the thiodiglycolic acid recovered in the reaction zone.   10. A process for the synthesis of thioglycolic acid, characterized in that it consists in bringing into contact, in a reaction zone, under a high pressure of at least about 17 bar at 34 bar formed by hydrogen sulphide. gaseous and at a temperature between room temperature and 600C, a mixture of monochloroacetic acid and dichloroacetic acid or their alkaline salts in a weight ratio of 99: 1 to 25 with a hydrosulfide of an alkali metal so that the molar ratio of the metal hydrosulfide to the monochloroacetic acid of said mixture is at least 2.1 and the dichloroacetic acid is at least 3.1, separating and recovering the thioglycolic acid from the   liquid produced from the reaction zone.   11. A process according to claim 10, characterized in that the ratio of mono- to dichloroacetic acid is from 98: 2 to 95: 5, the hydrosulfide of an alkali metal is sodium hydrosulfide, the ratio of   molar metal hydrosulfide to monochloro-   acetic acid is 2.1 to 3, the molar ratio of hydro-   metal sulphide with dichloroacetic acid is 3.1 to 4   and further separates and recovers thio acid   diglycolic liquid product of the reaction zone and reintroduces at least a portion of the acid   Thiodiglycolic acid recovered to the reaction zone.